Description

When charging electrochemical supercapacitors, redox electrochemical reactions take place in thin adsorption mono- and polymolecular films at the electrode-electrolyte interface. When being discharged, these same reactions occur in reverse. Thus, in electrochemical supercapacitors energy is stored in the form of internal energy of the surface compounds at the electrode-electrolyte interface. The characteristics of such energy storage devices depend to a large extent on the properties of the electrodes used and their designs. The main difference between electrochemical supercapacitors and the batteries is that electrochemical processes take place exclusively on the electrode's surface, which leads to higher rates of the electrochemical processes due to zero diffusion difficulties. The most serious drawback of electrochemical capacitors as compared with conventional supercapacitors (EDLCs) is the lower resistance of electrode materials to chemical and electrochemical degradation. This leads to a reduced maximum of charge-discharge cycles, amounting to several thousands or tens of thousands, depending on the type of electrode material.

The main advantage of electrochemical capacitors in comparison with their analogues is that they have potentially higher electrical capacitance at similar energy level. The specific electrical capacitance of the most advanced electrodes that are used in EDLCs usually does not exceed 300-400 F/g, while 600-700 F/g is not a limit for modern electrodes based on ruthenium oxides and hydroxides. Other well-known electrode materials to be used for electrochemical supercapacitors are nanocrystalline nickel and manganese oxides and hydroxides.

Modern electrochemical capacitors often have an asymmetrical structure, where one electrode accumulates energy in the electrical double layer, whereas the other accumulates energy through the Faraday processes. Thus, the positive aspects of supercapacitors and electrochemical supercapacitors are utilised. This type of electrochemical capacitor currently seems to be the most promising for further improvement.